The tactic, increasingly used in Florida's sensitive ecosystems, is known as "biological control."

You pit the good bug against a bad bug or weed and hope the good guy wins. But it isn't nearly that simple.

It is a complex practice involving many scientists, years of research and high hopes that the introduced predators don't do more harm than good.

Biological control is seen as an alternative to pesticides and herbicides, which are contributing to Florida's pollution problem.

The practice is more than 100 years old, and Florida researchers have been doing it for decades.

So far, they have unleashed about 70 predator species from other countries into Florida's environment, hoping to rid the state of pests such as alligatorweed, the pink hibiscus mealybug, citrus canker, hydrilla and, most recently, the Mexican "evil weevil," which threatens to wipe out the state's native bromeliads.

Nationwide, hundreds of such predator species have been released. The goal is to protect native species from falling victim to pests. Non-native plants and animals, also known as invasive exotics, compete for the same environment.

"What bugs me is that it's easy to bring in these exotics," said Bill Overholt, associate professor of entomology at the Norman C. Hayslip Biological Control Research and Containment Laboratory in Fort Pierce, part of the University of Florida's Institute of Food and Agricultural Sciences.

He said exotic plants are routinely brought into the state from other countries, many for the horticulture industry. About one exotic bug a month likely piggybacks and becomes established in Florida.

"To bring in a natural enemy to control that plant once it's become a problem is a really complex and time-consuming process," said Overholt, an advocate for stronger regulations on importing invasive exotics.

Researchers do lengthy studies to make sure the predator won't affect any species besides the targeted prey or cause other problems for Florida's environment.

It can take several years from field study to final widespread release if scientists discover the biological control seems to work.

In years past, there were unexpected consequences. Bugs went after different species than scientists intended. Or they reproduced so much they became a noxious pest themselves.

Success rates run about 30 percent, Overholt said, fueling criticism of such programs.

Pesticides are sometimes preferred because they are fast-acting.

"We aren't very patient as a species," Overholt said.

Not all dislike exotics

Though some view invasive exotics as damaging, others disagree.

Melaleuca, for instance, introduced from Australia as an ornamental, is described as "Florida's most infamous invasive species" by state officials. It clogged the Everglades, so in 1997, scientists introduced the melaleuca snout beetle, which feeds on melaleuca's stems and leaves. The tactic appears to be working.

Yet Florida's beekeepers say melaleuca is one of the state's top nectar producers because it blooms several times a year, providing food lacking elsewhere for honeybees. Beekeepers, who also sometimes rely on the exotic and typically unwanted Brazilian pepper tree for the same reason, usually oppose biological controls.

"They arbitrarily decide what's a weed," said longtime commercial beekeeper Bert Kelley of Polk County, secretary of the Florida State Beekeepers Association.

Today, scientists insist their methods are sophisticated and that they are considering what is best for entire ecosystems.

"All the mistakes all happened . . . years ago," said Ronald Cave, a researcher at the UF facility in Fort Pierce who discovered the franki fly -- a new solution to bugs attacking Florida's wild bromeliads. He also is studying two wasps he hopes might combat Asian cycad scale, which is wiping out the sago palm in Florida.

"It is no more appropriate to criticize modern biological control for disastrous introductions of the distant past than to criticize modern surgery for deaths through lack of antiseptic methods used in the past, but many have learned from such errors," said Cave's colleague, Howard Frank, a professor and entomologist at UF's Institute of Food and Agricultural Sciences, who is also working on the franki-fly project -- which is named after him.

Offering hope for crops

Biological control, some say, will be essential in the future, as the world population is projected to reach 8.9 billion by 2050.

Despite use of chemicals, 30 percent of all crops are lost to pests in developed countries, and presumably more in undeveloped nations. Biological controls are one way to attack pests with or without the cooperation of a landowner because bugs aren't confined to property lines.